Slimming Paint phase 2 compositing algorithm plumbing

Source/core/compositing/DisplayListCompositingBuilder.cpp

Index: Source/core/compositing/DisplayListCompositingBuilder.cpp
diff --git a/Source/core/compositing/DisplayListCompositingBuilder.cpp b/Source/core/compositing/DisplayListCompositingBuilder.cpp
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+++ b/Source/core/compositing/DisplayListCompositingBuilder.cpp
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/compositing/DisplayListCompositingBuilder.h"
+
+#include "platform/graphics/paint/DisplayItemTransformTreeBuilder.h"
+
+namespace blink {
+
+CompositedDisplayList DisplayListCompositingBuilder::build()
+{
+    // TODO(pdr): Properly implement simple layer compositing.
+    // See: https://docs.google.com/document/d/1qF7wpO_lhuxUO6YXKZ3CJuXi0grcb5gKZJBBgnoTd0k/view
+    (void)m_displayListDiff;
+    CompositedDisplayList compositedDisplayList;
+    DisplayItemTransformTreeBuilder transformTreeBuilder;
+    for (const auto& displayItem : m_displayItemList.displayItems())
+        transformTreeBuilder.processDisplayItem(displayItem);
+    compositedDisplayList.transformTree = transformTreeBuilder.releaseTransformTree();
+    return compositedDisplayList;
+}
+
+} // namespace blink